docs: def Muller_Steinhagen_Heck(m, x, rhol, rhog, mul, mug, D, roughness=0, L=1):
      r'''Calculates two-phase pressure drop with the Muller-Steinhagen and Heck
      (1986) correlation from [1]_, also in [2]_ and [3]_.
  
      .. math::
          \Delta P_{tp} = G_{MSH}(1-x)^{1/3} + \Delta P_{go}x^3
  
      .. math::
          G_{MSH} = \Delta P_{lo} + 2\left[\Delta P_{go} - \Delta P_{lo}\right]x
  
      Parameters
      ----------
      m : float
          Mass flow rate of fluid, [kg/s]
      x : float
          Quality of fluid, [-]
      rhol : float
          Liquid density, [kg/m^3]
      rhog : float
          Gas density, [kg/m^3]
      mul : float
          Viscosity of liquid, [Pa*s]
      mug : float
          Viscosity of gas, [Pa*s]
      D : float
          Diameter of pipe, [m]
      roughness : float, optional
          Roughness of pipe for use in calculating friction factor, [m]
      L : float, optional
          Length of pipe, [m]
  
      Returns
      -------
      dP : float
          Pressure drop of the two-phase flow, [Pa]
  
      Notes
      -----
      Applicable for  0 < x < 1. Developed to be easily integrated. The
      contribution of each term to the overall pressure drop can be
      understood in this model.
  
      Examples
      --------
      >>> Muller_Steinhagen_Heck(m=0.6, x=0.1, rhol=915., rhog=2.67, mul=180E-6,
      ... mug=14E-6, D=0.05, roughness=0, L=1)
      793.4465457435081
  
      References
      ----------
      .. [1] Müller-Steinhagen, H, and K Heck. "A Simple Friction Pressure Drop
         Correlation for Two-Phase Flow in Pipes." Chemical Engineering and
         Processing: Process Intensification 20, no. 6 (November 1, 1986):
         297-308. doi:10.1016/0255-2701(86)80008-3.
      .. [2] Mekisso, Henock Mateos. "Comparison of Frictional Pressure Drop
         Correlations for Isothermal Two-Phase Horizontal Flow." Thesis, Oklahoma
         State University, 2013. https://shareok.org/handle/11244/11109.
      .. [3] Thome, John R. "Engineering Data Book III." Wolverine Tube Inc
         (2004). http://www.wlv.com/heat-transfer-databook/
      '''
      # Liquid-only properties, for calculation of dP_lo
      v_lo = m/rhol/(pi/4*D**2)
      Re_lo = Reynolds(V=v_lo, rho=rhol, mu=mul, D=D)
      fd_lo = friction_factor(Re=Re_lo, eD=roughness/D)
      dP_lo = fd_lo*L/D*(0.5*rhol*v_lo**2)
  
      # Gas-only properties, for calculation of dP_go
      v_go = m/rhog/(pi/4*D**2)
      Re_go = Reynolds(V=v_go, rho=rhog, mu=mug, D=D)
      fd_go = friction_factor(Re=Re_go, eD=roughness/D)
      dP_go = fd_go*L/D*(0.5*rhog*v_go**2)
  
      G_MSH = dP_lo + 2*(dP_go - dP_lo)*x
      return G_MSH*(1-x)**(1/3.) + dP_go*x**3